High voltage utility transmission lines are capable of supplying power over tens or hundreds of miles (or further) with minimal losses because of the very high voltages used. Step-up transformers located at utility power generation plants boost the voltage transmission levels up, depending on the particular utility, to and beyond 745 kV AC. At high voltages, power can be transmitted effectively as power transmission is a function of voltage times the current times the cosine of the phase angle between the voltage and the current. Use of high voltage minimizes current in the lines which thus minimizes losses which can be generally expressed as current squared times the resistance of the transmission line (i.e., the conductor).
Electrical demand in the United States and worldwide has steadily grown. Larger and more conductors are needed. Utilities constantly upgrade their systems at choke points in the grid to add new conductors and/or to replace existing conductors with new conductors which may be able to carry more current. Conductor stringing apparatuses and processes are used between utility towers or poles which may be separated by large distances, for example, they may be a quarter of a mile to a half a mile apart.
In a conductor stringing operation, a device called a conductor or cable puller-tensioner is used. Two machines are necessary. One of the machines functions as a puller which supplies the energy to pull the conductor against the friction of fixtures on the poles, against the force of the cable by virtue of its mass and the earth's gravitational attraction (i.e., its weight) and against the resistance supplied by the other machine which functions as a tensioner. The tensioner is a necessary part of the equipment and process lest the cable/conductor would sag and get tangled up with foliage, trees or other structures located beneath the cable/conductor path.
Previously, a drum puller/tensioner was typically powered by an internal combustion engine driving a hydraulic pump. The resulting pressure and flow in the hydraulic system coupled with a mechanical gear reducer would rotate the drum at the specified torque and speed. Tensioning was hydraulically controlled. As the pulling rope began to rotate the drum, it created pressure in the hydraulic system that could be adjusted to create the desired line tension.
U.S. Pat. No. 3,326,528 to S. S. McIntyre entitled Cable Stringing and Tensioning System discloses at col. 3, lns. 34 et seq. “the operator of the vehicle initially energizes the stator coils with current that may be supplied from a storage battery 50. Eddy currents are then generated by the relative motion of rotors and stator that produce a magnetic field in the rotors. This tends to retard rotation of the rotors and shaft 40, and this retarding force on shaft 40 builds up through the train of gearing . . . and is transferred back therethrough the sheaves . . . to resist their turning for braking the outfeed of transmission cable thereover.”
Many high voltage utility transmission lines are located in or near cities. Some of these lines require periodic replacement and/or upgrade and considerable noise and pollution is generated by internal combustion engines which power existing conductor stringing puller-tensioners. The noise and pollution present nuisances for those living in proximity to the high voltage transmission lines. It is, therefore, desirable to have a conductor stringing apparatus which is environmentally compatible and efficient.